Acoustic and Perceptual
Effects of Rate and Loudness Manipulations in Dysarthria

K Tjaden

Rate
reduction and increased loudness are associated with an increase in the size of
the articulatory-acoustic working space, and thus improved acoustic
distinctiveness for speakers with dysarthria.Improved intelligibility also has been reported.Few studies have compared rate and loudness
effects for speakers with dysarthria, however, although these are common
treatment techniques.In the current
study, 15 speakers with dysarthria secondary to Multiple Sclerosis, 12 speakers
with dysarthria secondary to Parkinson disease (PD), and 15 healthy controls
read a passage in Habitual, Loud, and Slow conditions.Supraglottal behavior was inferred from the
acoustic measures. Ten listeners also scaled intelligibility of reading
passages, and intelligibility estimates were related to acoustic measures.Articulatory rate was reduced in the Slow
condition and vocal intensity increased in the Loud condition, relative to the
Habitual condition.Vowel acoustic
distinctiveness, as indexed by vowel space area, was maximized in the Slow
condition, but stop consonant acoustic distinctiveness, as indexed by first
moment difference measures, was maximized in the Loud condition.F2 slope measures for diphthongs were not
consistently affected by rate or loudness.Intelligibility for speakers with PD also improved in the Loud
condition.Intelligibility estimates,
however, were typically unrelated to acoustic measures of supraglottal behavior.Results are compared to previous studies and
implications for treatment are discussed.